1. Field of the Invention
The present invention relates to a settable mixture comprising magnesium oxide and magnesium chloride. The invention further relates to a method of manufacturing a sound insulating floor construction and to a sound insulating floor construction.
Mixtures of magnesium oxide and magnesium chloride, sometimes referred to as Sorel cement, are known in the art for application as binders for industrial floorings, for which purpose they are favored on account of high elasticity and bending tensile strength properties. It is also known in the art to manufacture lightweight building slabs comprising Sorel cement in combination with wood chippings.
2. Description of the Prior Art
International patent publication no. WO89/02422 discloses a settable magnesium cement composition comprising magnesium oxide, magnesium chloride and coarse fibrous long-stranded sawdust. In the composition suggested the content of magnesium chloride constitutes approximately one third of the content of magnesium oxide as measured by weight Suggested applications comprise use as a floor leveling compound or manufacture of moulded products such as tiles and the like. Particular advantages claimed with this composition comprise reduction of sweating, reduction of dust, better control over product quality, and sound attenuation among others.
German published patent application DE 41 08 562 suggests for a floor leveling compound a mixture of coarse wood chips with granulated foamed polystyrene together with ceramic aggregates and a hydraulic binder such as cement or plaster of Paris. The publication contains in respect of the ceramic aggregate also suggestions for expanded clay aggregate or pumice and others.
A publication "Lexikon der Technik" by Lueger, 1972, page 471 explains Sorel cement used for floor slabs. Filler materials, such as wood chips, paper, cork and stone powder, are mentioned. A solution of magnesium chloride is prepared to a density of 1.16 to 1.19.
A publication "Estriche und Bodenbelage Im Hochbau" by Diplom-Ing. Friedrich Eichler, VEB Verlag Technik Berlin, 1955, discloses a floor slab cast of Sorel cement on top of an insulation mat. Margin strips are arranged on the walls so as to separate the floor slab from the walls. The publication mentions Sorel cement with fillers, such as wood chips and stone powder. According to this publication, the floor slab must have a thickness of at least 5 cm for reason of structural considerations.
Applicant has found that Sorel cement is highly prone to expansion during setting. Relative expansions in the order of 1% are very likely. Given this rate of expansion a floor slab may, depending on dimensions and boundary constraints, crack and break up. The expansion takes place slowly but keeps growing over an extended period of time. This makes the expansion difficult to monitor accurately during the early stages and means that a risk of self-destruction is there for a long period.
The expansion propensity practically limits the use of Sorel cement to applications as a binder, to products cast in molds or to floor leveling compounds laid in comparatively thin layers and adhered to a floor base, which serves to keep the Sorel cement layer in position.
The applicant has found that the admixing of wood fibres in any substantial amount tends to make the mixture sticky and viscous and hence difficult to mix properly and difficult to apply. Improper mixing is detrimental to the structural integrity of the hardened product and likely to aggravate expansion problems.